Apparatus for machining by electro erosion



W 17, 1967 H. RHYNER ETAL. 3,343,915

APPARATUS FOR MACHINING BY ELECTRO EROSION Original Filed Nov. 8, 1962 INVENTORJS. H8772; F7: 7767'. /fewe Var MKJOM United. States. Patent 3,348,015 APPARATUS FOR MACHINING BY ELECTRO EROSION Heinz Rhyner and Rene Vors, Geneva, Switzerland, assignors to Ateliers des Charmilles S.A., Geneva, Switzerland, a corporation of Switzerland Continuation of application Ser.- No. 236,313, Nov. 8, 1962. This application Mar. 24, 1965, Ser. No. 442,468

6 Claims. (Cl. 219-69) This application is a continuation of our copending application No. 236,313, filed Nov. 8, 1962, and now abandoned.

In apparatus for machining by electro-erosion, a current source is connected to a work-piece and to an electrode by conductive line. It is generally known that the self-inductance of the electric lines connecting the source to the work-piece and the electrode stands in the way of very sharp current pulses. In order to maintain the selfinductance at acceptable values, it is necessary to place the current source very close to the electrode: this, however, is often impractical from a construction point of view.

It is the principal object of this invention to provide a low self-inductance conductor arrangement particularly adapted for use in electro-erosion machines.

, It is a further object of this invention to construct an electro-erosion machine in which the source can be placed at an appreciable distance from the zone of current utilization whilst permitting the flow of short and steep pulses to be maintained without any appreciable attenuation.

.- The illustration of this invention is in an electroerosion machine comprising a current source connected to an electrode and to a work-piece .by means of a conductive line which consists of a series of at least six conductors each one insulated against the other and having the same general direction. According to the invention, these conductors are divided into two. groups, all conductors of one group being parallel and arranged in such a way as to be distributed amongst the conductors of the other group which are equally parallel to each other, wherein one of these groups connects the electrode to the source, the other one joining the workpiece to the source. The attached drawing shows several embodiments and the details of the subject of the invention.

" FIG. 1 is a diagram of an electro-erosion machine.

FIG. 2 is a perspective view of a conductive line used in this machine.

FIGS. 3 to are transverse cross-sections of modifications of the line used in this machine.

The machine represented in FIG. 1 comprises an electrode 1 and a work-piece 2, both immersed in a dielectric liquid 3, held in a container 4 in a generally known way. The machine comprises a source 5 electrically connected to the electrode 1 and to the work-piece 2 by a line consisting of two cables 6 and 7.

As generally known in electrical engineering, the source 5 is intended to supply current impulses in order to produce successive spark discharges between the electrode and the work-piece, each of such sparks removing particles from the work-piece 2. The source 5 can, of course, be constituted, for instance, by a capacitor charged through a resistance and/or a selfinduction coil. Similarly, the source could be constituted by a pulse generating circuit as also used in electro-erosion machines.

The conductive line represented in FIG. 1 by cables 6 and 7 is formed, as shown in FIG. 2, by a series of flexible cable conductors, parallel to and insulated :from each other; these cables 8 to are arranged in a line. All these cables are embedded together in an insulating material 16 in form of a strip.

The cables 8, 10, 12 and 14 are parallelly connected 3,348,015 Patented Oct. 17, 1967 thus forming a group of cables which make up the conductor 6 whilst cables 9, 11, 13 and- 15, equally parallel connected form a group of cables making up conductor 7. According to the arrangement shown, two cables of one group are always separated by a cable of the other group, thus reducing greatly the coelficient of selfinduction. Due to the very low value of self-induction, it is possible to place the current source at a distance, placing it several meters away from the location of the electrode and work-piece whilst still permitting the flow of intense short spark currents. Furthermore, the row formed by the cables may be very flexible, which highly facilitates placing the cables into the desired position and all subsequent modifications of the position between the machine and the source. Finally, the cooling is better-- copper sections being equalthan in the case of a line formed by two conductors. This fact permits reducing the copper section required for the flow of a given current.

In case of the band comprising 12 conductors of 2 sq. mm. sections, each grouped in two sets of six conductors, which gives a line of 12 sq. mm. for the line, the selfinductance per unit of length ranges at 0.04 microhenry per meter.

By increasing the number of conductors, the coefficient of self-induction can be further reduced. In case of a band made up of conductors, arranged in one or several lines, these conductors having a section of 2 sq. mm. each and being connected to form two groups of 25 conductors, a specific self-induction of less than 0.01 pH per meter is obtained.

FIG. 3 shows in cross-section a modification of the conductive line intended to connect the source 5 to the electrode 1 and to the work-piece 2. According to this modification, the line is made up from 12 flexible cables, arranged in two sets of six each. The parallel cables indicated by the letter a, constitute one of the two conductors 6 or 7 of FIG. 1 whilst the other parallel cables indicated by the letter b make up the other of the said two conductors 6 or 7. Of course, lines comprising more than two rows could be provided and, in such embodi ments, it would be advantageous, in order to obtain the lowest possible coefficient of self-induction, to connect the cables in such away that a cable of one group (for instance a) would be adjacent to a cable of the other group b of the same row and that the nearest cable of the next row is a cable of the other group b.

FIG.- 4 represents a modification of a line constituted by a cable of circular section containing a great number of conductors a and b placed in such a way as to fill the whole section. In order to simplify the design, the conduc tors a are marked by a cross whilst the conductors b do not have a special mark of distinction. It can be seen that the parallel conductors a, are placed between the conductors b which are equally arranged parallelly to each other and to conductors a. By this arrangement, a conductor a is always placed next to at least one conductor b and vice versa.

FIG. 5 represents a variation with conductors a and b being constituted by parallel conductive deposits, for instance metal deposits, effected on both surfaces of a strip of insulating material 17. This strip may be very thin which, apart from higher mechanical flexibility, would give a very low self-induction per unit of length of the line thus constituted. One could, of course, place conductors on one of the strip surfaces only. Naturally these conductors could be covered by an insulating coating. A number of strips, each comprising conductors a and b on one surface, may be assembled in order to obtain a much thicker conductor.

It is obvious that the line could also be constituted by rigid conductors and that, in any case, each cable or each conductor could be insulated separately; all these insulated 3 cables could then be coupled and held together by any device so as to form a band comprising one or several rows of parallel conductors.

It should be remarked that the various lines described constitute transmission lines, the coefficient of self-induction of these lines per unit of length being, in first approximation, n times Weaker than that of a line of thesame section, but having only two conductors, n being the number of conductor pairs of the line. Compared to a classic line of two conductors, a line of the described type, With n conductor pairs presents a capacity n times higher and a characteristic impedance n times smaller. It follows from this that short and intense spark currents can be transmitted at a low voltage from the source to electrode and work-piece.

We claim:

1. In an electrical discharge machining apparatus for machining a conductive workpiece by a tool electrode across a dielectric coolant filled gap, a power supply having a pair of terminals each connectible to a different terminal of said gap, a low self-inductance conductor arrangement for providing short duration machining pulses of sharp rise and fall characteristic comprising a first group of conductors connected between one of said power supply terminals and one terminal of said gap to conduct power in one direction, a second group of conduotors connected between the other of said power supply terminals and the other terminal of said gap to conduct power in the opposite direction, said conductors electrically insulated one from the other and arranged in substantially parallel spaced relationship in a plurality of rows, each of said conductors in one group being axially aligned proximate with a conductor of the other group on at least one side in its own row and proximate with a conductor of the other group in each adjacent row.

2. The combination as set forth in claim 1 in which said rows of conductors are mounted in a concentric arrangement in a cable.

3. The combination as set forth in claim 1 in which said rows of conductors comprise spaced conductive deposits, mounted on both sides of a central insulating strip.

4. A low self-inductance electrical conductor arrangement for conducting short duration current pulses of sharp rise and fall characteristic from a power supply having a pair of terminals each connectible to a different terminal of a load, comprising a first group of conductors connected between one of said power supply terminals and one terminal of said load to conduct power in one direction, a second group of conductors connected between the other of said power supply terminals and the other terminal of said load to conduct power in the opposite direction, said conductors electrically insulated one from the other and mounted in substantially parallel relationship 4 in a plurality of rows, each of said conductors in one group being axially aligned proximate with a conductor of the other group on both sides in its own row and proximate wtih a conductor of the other group in each adjacent row.

5. A low self-inductance electrical conductor arrangement for conducting short duration current pulses of sharp rise and fall characteristic from a power supply having a pair of terminals each connectible to a different terminal of a load, comprising a first group of conductors connected between one of said power supply terminals and one terminal of said load to conduct power in one direction, a second group of conductors connected between the other of said power supply terminals and the other terminal of said load to conduct power in the opposite direction, said conductors electrically insulated one from the other and mounted in substantially parallel relationship in a plurality of concentric rows, each of said conductors in one group being axially aligned proximate with a conductor of the other group on both sides in its own row and proximate with a conductor of the other group in each adjacent row.

6. A low self-inductance electrical conductor arrange: ment for conducting short duration current pulses of sharp rise and fall characteristic from a power supply having a pair of terminals each connectible to a different terminal of a load, comprising a first group of conductors connected between one of said power supply terminals and one terminal of said load to conduct power in one direction, a second group of conductors connected between the other of said power supply terminals and the other terminal of said load to conduct power in the opposite direction, said conductors comprising spaced conductive deposits mounted in both sides of a central insulating strip in substantially parallel relationship in a pair of rows, each of said conductors in one group being axially aligned proximate with a conductor of the other group on both sides in its own row and proximate with a conductor of the other group in the adjacent row.

References Cited UNITED STATES PATENTS 1,551,275 8/1925 Wagner et al. 174-32 1,625,125 4/ 1927 Latour. 2,204,288 6/ 1940 Wilkolf 174-114 X OTHER REFERENCES Patrick, R. M. Flexible Strip Transmission Line, IBM Technical Disclosure Bulletin, volume 2, No. 6, pp. 3536 April 1960,

LEWIS H. MYERS, Primary Examiner. H. HUBERFELD, Assistant Examiner, 

1. IN AN ELECTRICAL DISCHARGE MACHINING APPARATUS FOR MACHINING A CONDUCTIVE WORKPIECE BY A TOOL ELECTRODE ACROSS A DIELECTRIC COOLANT FILED GAP, A POWER SUPPLY HAVING A PAIR OF TERMINALS EACH CONNECTIBLE TO A DIFFERENT TERMINAL OF SAID GAP, A LOW SELF-INDUCTANCE CONDUCTOR ARRANGEMENT FOR PROVIDING SHORT DURATION MACHINING PULSES OF SHARP RISE AND FALL CHARACTERISTIC COMPRISING A FIRST GROUP OF CONDUCTORS CONNECTED BETWEEN ONE OF SAID POWER SUPPLY TERMINALS AND ONE TERMINAL OF SAID GAP TO CONDUCT POWER IN ONE DIRECTION, A SECOND GROUP OF CONDUCTORS CONNECTED BETWEEN THE OTHER OF SAID POWER SUPPLY TERMINALS AND THE OTHER TERMINAL OF SAID GAP TO CONDUCT POWER IN THE OPPOSITE DIRECTION, SAID CONDUCTORS ELECTRICALLY INSULATED ONE FROM THE OTHER AND ARRANGED IN SUBSTANTIALLY PARALLEL SPACED RELATIONSHIP IN PLURALITY OF ROWS, EACH OF SAID CONDUCTORS IN ONE GROUP BEING AXIALLY ALIGNED WITH A CONDUCTOR OF THE OTHER GROUP ON AT LEAST ONE SIDE IN ITS OWN ROW AND PROXIMATE WITH A CONDUCTOR OF THE OTHER GROUP IN EACH ADJACENT ROW. 